Crystallization is an important technique to the biological and chemical arts. Specifically, a high-quality crystal of a target compound can be analyzed by x-ray diffraction techniques to produce an accurate three-dimensional structure of the target. This three-dimensional structure information can then be utilized to predict functionality and behavior of the target.
In theory, the crystallization process is simple. A target compound in pure form is dissolved in solvent. The chemical environment of the dissolved target material is then altered such that the target is less soluble and reverts to the solid phase in crystalline form. This change in chemical environment is typically accomplished by introducing a crystallizing agent that makes the target material less soluble, although changes in temperature and pressure can also influence solubility of the target material.
In practice however, forming a high quality crystal is generally difficult and sometimes impossible, requiring much trial and error and patience on the part of the researcher. Specifically, the highly complex structure of even simple biological compounds means that they are not amenable to forming a highly ordered crystalline structure. Therefore, a researcher must be patient and methodical, experimenting with a large number of conditions for crystallization, altering parameters such as sample concentration, solvent type, countersolvent type, temperature, and duration in order to obtain a high quality crystal, if in fact a crystal can be obtained at all.
Accordingly, there is a need in the art for methods and structures for performing high throughput screening of crystallization of target materials.
Microfluidic devices are defined as devices having one or more fluidic pathways, often called channels, microchannels, trenches, or recesses, having a cross-sectional dimension below 1000 μm, and which offer benefits such as increased throughput and reduction of reaction volumes. Interfacing microfluidic devices to macrosale systems, such as robotic liquid dispensing systems, has been challenging, often resulting in a loss of the number of reactions that can be carried out in parallel in a single microfluidic device. As a non-limiting example, Delucas discloses, among other things, using a microfluidic device to conduct nanoliter scale protein crystallization screening reactions in a parallel array format.
Unger discloses, among other things, microfluidic devices having an elastomeric block with a deflectable membrane. In one embodiment disclosed, which is depicted in FIGS. 1A and 1B, first elastomeric layer 1, having bottom surface 8 with microfabricated recess 2 formed therein, is bonded to top surface 7 of second elastomeric layer 3 having microfabricated recess 4 formed therein, to form an elastomeric block 5 having a first channel 6 formed from the recess 2 of the first elastomeric layer 1 being closed off by top surface 7 of second elastomeric layer 3, and where recess 4 of the second elastomeric layer is overlapped by first channel 6 formed, deflectable membrane 8 is formed by a portion of second elastomeric layer 3 separating first channel 6 from recess 4 of second elastomeric layer 3. Elastomeric block 5 may then be attached to substrate 9 so that recess 4 of second elastomeric layer 3 forms second channel 10 with a top surface of substrate 9. Fluid flow through second channel 10 may be controlled by actuating deflectable membrane 8 to deflect into and out of second channel 10. Deflectable membrane 8 may be actuated by increasing or decreasing the fluid pressure in first channel 6 to cause deflectable membrane 8 to deflect into or out of second channel 10, respectively. Alternatively, by increasing or decreasing the fluid pressure in second channel 10, deflectable membrane 8 can be deflected into or out of first channel 6, respectively.
FIG. 1C depicts the use of the device just described wherein liquid is introduced into second channel 10 through via 11, which was made by coring a fluid path from the top of the elastomeric block through first elastomeric layer 1 part of second elastomeric layer 3 into second channel 10. The fluid filling second channel 10 could then be partitioned by applying fluid pressure, such as gas pressure, through second via 13, which was made by coring through first elastomeric layer 1 into first channel 6 so that when the pressure was increased in first channel 6, deflectable membrane 8 deflected down into second channel 10 to contact the surface of substrate 9. Particular devices of Unger provide for high-density, reliable microfluidic devices in which the movement of fluid therein could be evoked and/or regulated by actuating the deflectable membrane to cause the membrane to function as part of a valve or pump.
An ideal application for microfluidic devices is screening for conditions that will cause a protein to form a crystal large enough for structural analysis. Protein crystallization is an important step in determining the structure of such proteins. Typically, reactions were set up by manually pipetting a solution containing a protein and a solution containing a protein crystallization reagent to cause the protein to form a crystal large enough to place in line with an X-ray source to perform X-ray diffraction studies. Determining the right conditions that will form a large enough crystal is often determined by seemingly countless trial and error experiments. Consequently, precious protein isolates are exceedingly limited in supply and therefore need to be judiciously used while screening for the right crystallization conditions. As a way to spare protein consumption during condition screening, efforts were made to reduce the volume of protein crystallization assays while increasing the number of experiments performed in parallel during the screen. Delucas discloses, among other things, methods and devices for carrying out nanoliter scale (nanoscale) protein crystallization experiments. In one embodiment disclosed, a microfluidic device is used to carryout nanoscale protein crystallization experiments in wells formed in a substrate.
Hansen discloses, among other things, microfluidic devices for carrying out protein crystallization reactions. Some of the embodiments disclosed in Hansen employ Unger's elastomeric block having deflectable membranes therein to regulate fluid flow. For example, a microfluidic device having a first chamber containing a solution of a protein is in fluid communication with a second chamber containing a solution containing a crystallizing agent that when contacted with the protein in the first chamber, may induce that protein to form crystals. In one example of many, the fluid communication between each chamber is through one or more channels. A valve situated between each of the chambers and in communication with the channel can be actuated to regulate the diffusion between the two chambers. The first chamber is in communication with a first inlet for introducing the solution containing the protein into the first chamber, and the second chamber agent is in communication with a second inlet for introducing the crystallization agent into that chamber.
Hansen discloses, among other things, a carrier for holding the microfluidic device of Hansen. An example of the Hansen carrier is shown in FIG. 2 where microfluidic structure 11000, which has several inlets and inlet rows such as well row 11012a and well row 11012b, sample inlet 11012c and containment valve control inlet 11012d and interface valve control inlet 11012e, is placed inside a frame base 11002 in receiving area 1106 having view window 1103 therein. Top frame 11014, which has pressure cavities 11026 and 11024 is placed upon frame base 11002 with microfluidic structure 11000 sandwiched between so that each pressure cavities seals against well rows 11012a and 11012b to form pressure chambers on top of each well row. In use, each well in well rows 11012a and 11012b are typically filled with different reagents for crystallizing proteins and sample inlet 11012c is loaded with a sample solution containing a protein to be crystallized. Containment valve control inlet 11012d and interface valve control inlet 11012e are typically filled with a liquid, such as an oil or water, to hydraulically actuate the valves in the microfluidic device. Pneumatic lines are inserted into control inlets 11012d and 11012e to apply pressurized gas in fluidic communication with the liquid contained within each control inlet channel within the microfluidic device, which in turn deflect membrane valve at certain intersections between the channels of the first elastomeric layer and the second elastomeric layer, as shown in FIG. 1.
Likewise, sample solution can be driven into a channel and on into chambers inside the microfluidic device by similarly applying gas pressure to the sample inlet 11012c to cause the sample solution to develop hydraulic pressure to move it through the channel into the chambers. Reagents loaded into wells of well row 11012a and 11012b can also be driven into their corresponding channels and on into chambers inside the microfluidic device by applying gas pressure to each of the pressure cavities. Once each of sample and reagent chambers within the microfluidic device have been filled, containment valves may be then closed by actuating deflectable membranes in communication with the inlet channel preceding the chamber to keep the sample and reagents inside their corresponding chambers. Meanwhile, an interface valves between each of the sample/reagent chamber pairs is kept closed to keep the reagent from diffusing into the sample and the sample from diffusing into the reagent chambers. After the filling of all chambers is complete, free interface diffusion can begin by opening the interface valves, while keeping the containment valves closed.
Protein crystallization experiments performed using the devices disclosed in Hansen may take several days to perform. As mentioned, the containment valves must be kept closed at all time to prevent sample or reagents from moving out of the chambers, potentially cross-contaminating each other. Accordingly, a source of pneumatic pressure to create a constant source of hydraulic pressure need be maintained to keep the containment valves closed. This can be done by having an “umbilical cord” connecting the carrier connected to a source of gas pressure such as a regulated gas supply. However, such umbilical cords may limit a user's ability to move a carrier about a laboratory, for example, into a refrigerator or incubator to achieve temperature control. Thus, there is a need for a system that would liberate a microfluidic device, such as those described by Hansen or Unger, from the apparent need for an umbilical cord to maintain valve actuation.
Schulte et al. (“Schulte”), U.S. Patent Publication No. 2003-0034306 A1, published on Feb. 20, 2003, entitled “Well-Plate Microfluidics,” which is hereby incorporated by reference for all purposes, discloses microfluidic devices, however, there are numerous and substantial differences between the invention disclosed herein and the devices of Schulte.